1. Technical Field
The present invention relates generally to optical communication and/or data transmission systems.
2. Description of Related Art
Optical communication systems transmit data using electromagnetic light signals in optical fiber and/or free space (for example, building to building, ground to satellite, satellite to satellite, etc.). The electromagnetic carrier wave is modulated to carry the data. Optical communication in optical fiber typically involves: generating the optical signal, relaying the signal on an optical fiber (including measures to reduce/mitigate attenuation of, interference with and/or distortion of the light signal), processing a received optical signal, and converting the signal into a useful electrical signal. Transmitters can be semiconductor devices such as laser diodes, producing coherent light for transmission. A number of receivers have been developed for processing a transmitted lightwave optical signal to provide processed optical signal input(s) to one or more photodetectors, which convert light into electricity.
A coherent receiver converts a modulated optical signal into four electrical signals corresponding to the “in-phase” (I) and “quadrature” (Q) optical signal components of the two optical polarization states, which together carry all or nearly all of the information conveyed by the optical signal. These components can be processed to recover the optically transmitted data regardless of modulation type. A simple coherent receiver is composed of a local-oscillator laser, an optical coupler, and one or more photodetectors that can be in a “balanced” configuration that cancels photocurrents and eliminates DC terms and the related excess intensity noise.
Systems, methods and techniques that provide improved ways to process optical signals in an optical communication systems, including signals used for testing, analysis, diagnostic uses and as a receiver in a more general sense would represent a significant advancement in the art.